A Simple Approach to Eliminate Occasional Grass Formation in ICP Backside Via Etch Process

Joe Zhou, Daniel Hou, Cindy Lee, Ahmad Ranjbari 
GCS, Inc. 22315 Kashiwa Court, Torrance, CA  90505 
Email: Jzhou@gcsincorp.com, Phone: 310-530-7274m Fax: 310-530-7279

 ‘Grass’ formation is the very common defects for via etch process when using a BC13/C12 as basic gases in an inductively coupled plasma (ICP) system  Presence of grass can potentially degrade device performance due to poor metallization coverage.  In this study we found that grass formation strongly depends on GaAs surface condition prior to etch.  Any surface contaminants, such as photo resist residues and/or scumming can contribute to grass formation.  We found that applying suitable chemical clean and 02 plasma descum prior to via etch process would prevent the grass formation.  To avoid changes to via profile and/or etch rate, etch parameters were not altered in this study. 

Keywords:  GaAs devices, backside, via etch, grass formation

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